Feed roller type system for continuous feeding of filler material for friction stir welding, processing and fabrication

ABSTRACT

The present invention relates to tools and methods for disposing, coating, repairing, or otherwise modifying the surface of a metal substrate using frictional heating and compressive/shear loading of a consumable metal against the substrate. Embodiments of the invention include friction-based fabrication tooling comprising a non-consumable member with a throat and a consumable member disposed in the throat, wherein consumable filler material is capable of being introduced to the throat in a continuous manner during deposition using frictional heating and compressive/shear loading of the filler material onto the substrate. Preferred embodiments according to the invention include such tools operably configured for applying a force or displacement to the filler material during deposition. Especially preferred embodiments can include using various powder-type consumable materials or combinations during the deposition process to obtain a continuous compositional gradient in the filler material yielding a functionally graded coating on the substrate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional Application of U.S. application Ser.No. 13/442,201 (“the '201 application”), filed Apr. 9, 2012. The '201application is a Continuation-in-Part (CIP) application of U.S.application Ser. No. 12/792,655 (“the '655 application”), filed Jun. 2,2010. The '655 Application is a CIP application of U.S. application Ser.No. 11/527,149 (“the '149 application”), filed Sep. 26, 2006. The '149application claims priority to and the benefit of the filing date ofU.S. Provisional Application No. 60/720,521, filed Sep. 26, 2005. The'201 application is a CIP application of U.S. application Ser. No.12/987,588 (“the '588 application”), filed on Jan. 10, 2011. The '588application claims priority to and the benefit of the filing date ofU.S. Provisional Application No. 61/293,543, filed Jan. 8, 2010. The'588 application is a CIP application of the '655 application, which isentitled to the chain of priority identified above. The '201 Applicationclaims priority to U.S. Provisional Application No. 61/472,918, filedApr. 7, 2011 and U.S. Provisional Application No. 61/473,221, filed Apr.8, 2011. The disclosure of each of the applications identified above ishereby incorporated by reference herein in their entireties.

STATEMENT OF GOVERNMENT INTEREST

This invention was supported by the U.S. Office of Naval Research underContract No. N00014-05-1-0099. The U.S. Government has certain rights inthis invention.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to tools and methods for disposing,coating, repairing, or otherwise modifying the surface of a metalsubstrate using frictional heating and compressive/shear loading of aconsumable metal against the substrate. More particularly, embodimentsof the invention include friction-based fabrication tooling comprising anon-consumable member with a throat and a consumable member disposed inthe throat, wherein consumable filler material is capable of beingintroduced to the throat in a continuous manner during deposition usingfrictional heating and compressive/shear loading of the filler materialonto the substrate.

2. Description of Related Art

Conventional coating techniques, such as flame spray, high-velocityoxygen fuel (HVOF), detonation-gun (D-Gun), wire arc and plasmadeposition, produce coatings that have considerable porosity,significant oxide content and discrete interfaces between the coatingand substrate. Typically, these coating processes operate at relativelyhigh temperatures and melt/oxidize the material as it is deposited ontothe substrate. Such conventional techniques are not suitable forprocessing many types of substrates and coating materials, such asnanocrystalline materials due to the grain growth and loss of strengthresulting from the relatively high processing temperatures.

An alternative deposition process available is referred to as cold spraytype depositing. Such techniques typically involve a relativelylow-temperature thermal spray process in which particles are acceleratedthrough a supersonic nozzle. These techniques, however, may berelatively expensive and/or generally incapable of processing highaspect ratio particles, such as nanocrystalline aluminum powder producedby cryomilling. As a result, products prepared using cold spraytechniques typically contain oxide impurities.

In light of these drawbacks, the inventors have developed new coatingdeposition techniques by having designed various friction-basedfabrication tools capable of depositing coatings on substratesefficiently and in a simple manner. For example, the inventors havedeveloped a tool comprising a non-consumable body and a throat defininga passageway lengthwise through the body, which are shaped to deliver aconsumable material to a substrate and form a coating on the substrateusing compressive loading and frictional heating. Such tools are capableof resulting in high quality adhesions between the substrate and coatingand high strength products having an increased resistance to failure. Inaddition, the inventors have developed tools having internal toolgeometry and means for exerting normal forces on the consumable duringrotation to further enhance the tool's capability of delivering ordepositing the feed material to or on the substrate.

The inventors have made further advancements in this field by reducingthe effect of some of the mechanical challenges presented by feedingsolid material into a spindle, including reducing down time of themachinery due to build up of consumable material within the spindle,improving efficiency of the deposition process by finding ways tocontinuously introduce consumable material to the tool, and bydeveloping processes for introducing variations in the composition ofthe feed material during the deposition process for preparingfunctionally graded substrates in a simplified manner.

Such advancements in the coating field have made digital manufacturingby friction stir fabrication of specialty alloys a possibility.State-of-the-art digital manufacturing technologies for metal parts haveevolved around powder metallurgy and fusion welding-based processes.Both of these processing methodologies yield parts with inferiormechanical and physical properties as compared to wrought metal of thesame composition. Additionally, the production rates for even thefastest processes are relatively low (˜40 lbs/hr for Ti) and the partenvelopes are limited to a few cubic feet.

To address some of these particular manufacturing difficulties, thepresent inventors have proposed a novel high-speed, large-volume wroughtmetal deposition technology capable of enabling affordable,full-density, near net-shape component manufacturing from a wide rangeof alloys, including specialty high-strength steels and ultrafine-grained alloys. The ability to rapidly fabricate complex wroughtalloy components from the ground up will provide a leap-aheadadvancement in digital manufacturing and combat readiness.

SUMMARY OF THE INVENTION

Provided by embodiments of the invention is a highly scalable processfor coating, joining direct digital manufacturing of wrought metalstructures based on friction stir fabrication (FSF) processes. Usingthese state-of-the-art techniques it is possible to producehigh-strength coatings, welds, and structures (strengths comparable tothe base metal UTS), while retaining a wrought microstructure. Theinventive structures exhibit superior qualities compared to structureshaving a solidification microstructure (i.e. cast microstructure).Benefits of the invention include the capability of creating substrateswith little to no porosity, a typical undesirable result of partsprepared using molds.

Methods within the scope of the invention, and tools for performing suchmethods, include: depositing a coating on a substrate by way offrictional heating and compressive loading of a coating material againstthe substrate; continuously delivering the coating material through astirring tool during frictional heating and compressive loading; andforming and shearing a surface of the coating on the substrate. The feedmaterial or coating material can be fed through the spindleno-continuously, semi-continuously, or preferably continuously. Suchmethods and tools include use of tools comprising a surface facing thesubstrate for forming and shearing a surface of the coating, such as ashoulder.

Such methods can comprise depositing the coating material by spreadingthe coating material across the substrate by translating, relative toone another, a stirring tool and the substrate, wherein the stirringtool comprises a shoulder for trapping and shearing coating materialbelow the shoulder. In embodiments, a coating material is deposited on asubstrate using frictional heating and compressive loading of thecoating material against the substrate. The coating material is aconsumable material, meaning as frictional heating and compressiveloading are applied during the process, the coating material is consumedfrom its original form and is applied to the substrate. Forcontinuous-feed applications, it is preferred that the feed material bein the form of a powder or pellet. More particularly, as the appliedload is increased, beyond what would be required to join the consumablecoating material to the substrate, and the portion of the coatingmaterial adjacent to the substrate is caused to deform under thecompressive load. In preferred embodiments, the deformed metal is thentrapped below a rotating shoulder of the friction-based coating tool andthen sheared across the substrate surface as the substrate translatesand rotates relative to the tool.

Even further, the depositing can comprise pressing and translating thecoating material against and across the substrate while rotating thecoating material with a stirring tool which causes frictional heating ofthe coating material and substrate.

Preferred embodiments according to the invention include friction stirtools operably configured for applying a force or displacement to thefiller material during deposition. Further preferred embodiments ofmethods, tools and systems of the invention include those in which thecoating material is consumable and the stirring tool is non-consumable.For example, the coating material can be in powder form.

The stirring tool and coating material can be configured to rotaterelative to the substrate. Rotation of the tool relative to thesubstrate can be in addition to translation of the tool relative to thesubstrate. Likewise, the stirring tool can have a throat and the coatingmaterial can be delivered through the throat of the stirring tool.

More specific embodiments of methods, systems, and tools according tothe invention can include a tool with a throat, where the coatingmaterial and throat are operably configured to provide for continuousfeeding of the coating material through the throat of the stirring tool.In preferred embodiments, the consumable material is a powder, thethroat of the tool is a hollow cylinder, and an auger shaped memberdisposed within the throat of the tool is used to force consumablepowder material through the throat of the tool onto the substrate. Thecoating material can be delivered by pulling or pushing the coatingmaterial through the throat of the stirring tool.

Methods of the invention can comprise depositing coating material byplastically deforming and combining both a portion of the coatingmaterial and a portion of the substrate to form a coating on thesubstrate in a volume between the stirring tool and substrate and cancomprise shearing of the surface of the coating by frictional heatingand compressive loading of the coating while between the stirring tooland the substrate.

Preferred embodiments can comprise a friction stir tool comprising: anon-consumable body formed from material capable of resistingdeformation when subject to frictional heating and compressive loading;a throat with an internal shape defining a passageway lengthwise throughthe non-consumable body; an auger disposed within the tool throat withmeans for rotating the auger at a different velocity than the tool andfor pushing powdered coating material through the tool throat; wherebythe non-consumable body is operably configured for imposing frictionalheating and compressive loading of the consumable coating materialagainst a substrate, and comprises a surface for trapping the consumablecoating material in a volume between the non-consumable body and asubstrate, and for forming and shearing a surface of the coating on thesubstrate.

Further preferred is a friction stir tool as described having a throatsurface, which is a hollow cylinder disposed lengthwise through the toolbody.

An embodiment of the present invention provides a friction-basedfabrication tool comprising: a non-consumable body formed from materialcapable of resisting deformation when subject to frictional heating andcompressive loading and a throat defining a passageway lengthwisethrough the body and comprising means for delivering a coating materialthrough the throat of the tool throat.

Other specific embodiments include friction-based fabrication toolscomprising: (a) a spindle member comprising a hollow interior forhousing a coating material disposed therein prior to deposition on asubstrate; (b) means for dispensing coating material through the throatof the tool; (c) means for compressive loading of the coating materialfrom the spindle onto the substrate; and (d) means for rotating andtranslating the spindle relative to the substrate; wherein the spindlecomprises a shoulder surface with a flat surface geometry or a surfacegeometry with structure for enhancing mechanical stirring of the loadedcoating material, which shoulder surface is operably configured fortrapping the loaded coating material in a volume between the shoulderand the substrate and for forming and shearing a surface of a coating onthe substrate. In preferred embodiments, means for dispensing coatingmaterial through the throat of the tool is an auger shaped memberdisposed lengthwise in the throat and operably configured for pushingpowdered coating material through the tool throat.

Further provided are tooling configurations comprising any configurationdescribed in this application, or any configuration needed to implementa method according to the invention described herein, combined with aconsumable coating material member. Thus, tooling embodiments of theinvention include a non-consumable portion (resists deformation underheat and pressure) alone or together with a consumable coating materialor consumable filler material (e.g., such consumable materials includethose that would deform, melt, or plasticize under the amount of heatand pressure the non-consumable portion is exposed to).

Another aspect of the present invention is to provide a method offorming a surface layer on a substrate, such as repairing a marredsurface, building up a surface to obtain a substrate with a differentthickness, joining two or more substrates together, or filling holes inthe surface of a substrate. Such methods can comprise depositing acoating material on the substrate with tooling described in thisapplication, and optionally friction stirring the deposited coatingmaterial, e.g., including mechanical means for combining the depositedcoating material with material of the substrate to form a morehomogenous coating-substrate interface. Depositing and stirring can beperformed simultaneously, or in sequence with or without a period oftime in between. Depositing and stirring can also be performed with asingle tool or separate tools, which are the same or different.

In embodiments, the tool and auger preferably rotate relative to thesubstrate. In further preferred embodiments, the tool and auger rotaterelative to one another, i.e., there is a difference in rotationalvelocity between the auger and the tool body. There may be some relativerotation between the powder coating material and the substrate, tool, orauger. The coating material and tool are preferably not attached to oneanother to allow for continuous or semi-continuous feeding or depositionof the coating material through the throat of the tool.

Especially preferred embodiments can include using various powder-typeconsumable materials or combinations during the deposition process toobtain a continuous compositional gradient in the filler materialyielding a functionally graded coating on the substrate. Included insuch embodiments are methods, tooling, and systems which make possiblethe fabrication of specialty substrates by digital manufacturing usingfriction stir fabrication-based techniques.

Embodiments of metal deposition methods according to the invention maysignificantly reduce labor and time requirements for preparingsubstrates having a desired composition. For example, the coatingmaterial to be deposited on the substrate may be delivered to thesubstrate surface using a “push” method, where a rotating-plunging tool,e.g., auger, pushes the filler material through the rotating tool, suchas a spindle. Feed material can be introduced to the tool in variousways, including by providing an infinite amount of powder fillermaterial into the tool body from a refillable container in operablecommunication with the tool.

In preferred embodiments, the filler material is a powdered solid and isfed through the tool body using an auger shaped plunging tool (e.g., athreaded member). In such an embodiment, the plunging tool may or maynot be designed to move or “plunge” in a direction toward the substrate.For example, the threaded configuration of the auger itself is capableof providing sufficient force on the powdered feed material to directthe consumable toward the substrate for deposition, without needingvertical movement of the auger relative to the tool.

As the spindle and plunging tool rotate, compressive loading andfrictional heating of the filler material can be performed by pressingthe coating material into the substrate surface with the downward force(force toward substrate) and rotating speed of the plunging tool.

During the deposition process, it is preferred that the spindle rotateat a slightly slower rate than the auger or plunging tool.Alternatively, in embodiments, the spindle can also be caused to rotatefaster than the auger. What is important is that there is relativerotation between the spindle and the auger during deposition of thecoating material. Due to the difference in rotational velocities, thethreaded portion of the auger provides means for pushing the consumablematerial through the tool body to force the material out of the tooltoward the substrate. The threads impart a force on the feedstock thatpushes the feed material toward the substrate much like a linearactuator or pneumatic cylinder or other mechanical force pushing on asurface of the feedstock. Even further, it may be desired in someapplications to alter the rotational velocity of the tool body and/orauger during deposition of the coating material.

Deposition rate of the filler material on the substrate can be adjustedby varying parameters such as the difference in rotational velocitybetween the auger screw and the spindle, or modifying the pitch of thethreads on the auger. If desired, for particular applications it may bewarranted to control filler material temperature inside or outside ofthe tool body. Such thermally induced softening of the filler materialprovides means to increase deposition rates to meet applicationrequirements.

While this process has been demonstrated on materials such as HY80steel, the inventors have further expanded this approach to enable 3Dpart buildup. Fabrication of large parts in a timely manner can beaccomplished with the continuous powder feeding mechanism. Multiplebenefits and advantages can be realized from the inventive digitalmanufacturing technology as compared with other traditional methods.Table 1 shows some of these benefits.

TABLE 1 Comparison of various digital manufacturing technologies.Friction Stir Laser Sintering/ Laser Deposition E-Beam - UltrasonicFabrication Melting (LENS etc.) Powder Bed Welding Multi-material partsx x x Wrought x x microstructure Complex geometries x x x x Full densityx x Layer-to-layer bond x strength comparable to base metal UTS Enablesjoining of parts x x x Wrought mechanical x x and physical propertiesContamination prone no yes yes yes no

Provided by embodiments of the invention is the ability to combinecomplex-geometry-fabrication with multi-functional, multi-materiallayered composite structures with little or no discrete interfacebetween layers. Additional capabilities include the ability to fabricatefunctionally graded structures by local compositional variation,controlling microstructure by locally varying processing conditions suchas total heat input and applying specialized surface treatments andcoatings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate certain aspects of some of theembodiments of the present invention, and should not be used to limit ordefine the invention. Together with the written description the drawingsserve to explain certain principles of the invention.

FIG. 1 is a schematic diagram illustrating a continuous feeding systemof the invention.

FIG. 2A is a schematic diagram illustrating exemplary auger screws ofthe invention.

FIG. 2B is a schematic diagram illustrating a continuous feed systemaccording to embodiments of the invention using a conical auger screw.

FIGS. 3A-B are schematic diagrams showing a friction-based fabricationprocess of the invention.

FIG. 4 is a schematic diagram of a digital manufacturing method of theinvention.

FIG. 5 is a schematic diagram of a continuous feeding system of theinvention which uses a rolling mill type mechanism.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS OF THE INVENTION

Reference will now be made in detail to various exemplary embodiments ofthe invention. It is to be understood that the following discussion ofexemplary embodiments is not intended as a limitation on the invention.Rather, the following discussion is provided to give the reader a moredetailed understanding of certain aspects and features of the invention.

Embodiments of the present invention provide a system to continuouslyfeed powdered or granular materials through a friction stir fabricationor friction stir welding spindle. In the context of this specification,the terms “powdered,” “granular,” “pellet,” “particle,” and the like areintended to encompass a form in which the coating material can beprovided as solid, loose particles. Each of these terms may be usedinterchangeably.

One challenge is that since the filler material is keyed into thespindle at the tool tip to ensure that the material is being rotatedwith the tool, it is preferred that the material fed into the spindlealso be rotating at the same speed and aligned with the key orientation.For the filler material to be fed continuously into and through the toolbody, a constant force or displacement should be applied to the fillermaterial. In the context of this specification, the terms “fillermaterial,” “coating material,” “consumable material,” “feed material,”and the like may be used interchangeably to refer to the material thatis deposited on the substrate from the friction fabrication tooling. Inan embodiment, a powder filler material is used in combination with anauger disposed in the tool throat for applying a constant displacementto the filler material within the throat.

The coating/filler material (for example, powder) can be fed through therotating spindle where frictional heating occurs at the filler/substrateinterface due to the rotational motion of the filler and the downwardforce applied. The mechanical shearing that occurs at the interface actsto disperse any oxides or boundary layers, resulting in a metallurgicalbond between the substrate and coating. As the substrate moves (or withany relative motion between the substrate and tool), the coating can beextruded under the rotating shoulder of the tool. Typical translationspeeds are approximately 1-3 inches per minute, however, with particulartool design and/or materials being used, it is possible that thetranslation speed could be increased to 10 inches per minute or faster.

According to embodiments, the present invention provides afriction-based fabrication tool comprising: a non-consumable body with athroat; a screw-type auger disposed in the throat for continuouslydelivering coating material through the throat of the tool body; one ormore means for rotating the tool body at a desired first velocity andfor rotating the auger at desired second velocity; and wherein the toolbody comprises a surface for trapping coating material loaded on thesubstrate in a volume between the tool body and the substrate and forforming and shearing a surface of a coating on the substrate withfrictional heating and shear loading. In preferred embodiments, suchtooling can comprise a throat which is generally the shape of a hollowcylinder. Even further, the tooling can comprise a sleeve, which is atubular member disposed within the tool throat and within which theauger is disposed.

Friction-based fabrication according to embodiments of the invention caninvolve depositing material onto a substrate and subsequently stirringthe material into the substrate using friction stir processing tohomogenize and refine the microstructure. Certain advantages of thissolid-state process include, but are not limited to, the capability ofdepositing coatings, including nanocrystalline aluminum and/or metalmatrix composites and the like, onto substrates such as aluminum atrelatively low temperatures. The capability to deposit the substrates atsuch low temperatures allows for the ability to use a broader range ofsubstrates, thereby being able to form improved friction stir tools formultiple applications.

In accordance with an embodiment of the present invention, the coatingmaterial may be deposited on the substrate at a temperature below amelting temperature of the coating material. The depositing (e.g.,loading) of the coating material can be performed using one or moremethod steps for example described above. Loading of the coatingmaterial onto the substrate may be performed at a temperature rangingfrom about 100 to 500° C. or more below the melting point of the coatingmaterial. When the coating material comprises Al, the material may bedeposited on a substrate at a temperature below about 500° C., typicallybelow about 400° C. Once the coating material is initially loaded ontothe substrate, any subsequent friction stirring of the coating materialand/or substrate material may also preferably be performed below themelting temperature of the coating material. For example, when thecoating material comprises Al, friction stirring temperatures may bemaintained below about 500° C., typically below about 400° C.Furthermore, the friction stirring process(es) may be performed at atemperature below a melting temperature of the substrate.

Coatings produced using friction-based fabrication have otheradvantages, such as superior bond strength, density, and lower oxidecontent as compared to other coating technologies in use today. Thesefriction-based fabrication processes may also be used to fill holes invarious types of substrates, thereby making them stronger.

Embodiments provide for a tool comprising means for causingtranslational movement of the tool body relative to the substrate.Metallurgical bonding and/or homogenization and/or refinement of themicrostructure between the substrate and coating can be achieved throughrotation and/or translation or other relative movement between the tooland substrate. Such relative movement between substrate and tool,combined with means for compressing and retaining the coating materialbetween the substrate and tool, can add additional frictional heating tothe system. Likewise, the surface geometry of the tool can be modifiedto provide increased frictional processing of the materials, such as atool with a shoulder and/or one or more pin-type projections, or aseparate friction stir type tool. Frictional heating, compressiveloading, and mechanical stirring are factors that can be adjusted toachieve a particular result.

Means for rotating the auger and tool body can be operably configuredfor rotation in the same direction or opposing directions. Preferably,the auger and tool body are rotated in the same direction, but atdifferent speeds, so that there is relative rotation between them.

In preferred embodiments, the auger is operably configured fordelivering coating material in powder form through the tool body.

More specifically, to overcome the mechanical challenges of feedingsolid material into the rotating keyed spindle, a mechanism as shown inFIG. 1 was conceived to feed powder into the spindle and force it out ofthe spindle while ensuring the filler is keyed into the spindle. Thissystem utilizes an auger screw to force powder through the spindle at adefined rate, which is one means capable of accomplishing this purpose.Additional methods of feeding solid stock keyed into the orientation ofthe spindle and rotating at the exact rate of the spindle areconceivable. For example, force can be applied to the filler materialusing a metal rolling mill type mechanism which is rotating with thespindle, as shown in FIG. 5.

In such an embodiment, the spindle is spinning at a desired rotationalvelocity and the auger screw is driven at a different rotational speedin the same rotational direction which acts to force material out of thespindle. As shown in FIG. 1, the angular rotational speed or velocity ofthe friction stir tool is identified as ω1 and the angular rotationalvelocity of the auger is identified as ω2. In the context of thisspecification, the terms “rotational speed,” “rotational velocity,”“angular speed,” and “angular velocity” can be used interchangeably andrefer to the angular velocity of a component of the tool during use. Theauger screw can rotate at a slower speed than the spindle, or inpreferred embodiments the auger screw can rotate faster than thespindle. What is important is that there is relative rotation betweenthe spindle and auger to cause filler material to be forced through thethroat of the tool.

The pitch of the threaded auger screw and the volumetric pitch rate ofthe screw will affect the deposition rate under certain circumstances,and can be modified to accomplish particular goals. It is within theskill of the art to modify the pitch of the threads on the auger toobtain a certain desired result. The terms “tool,” “friction stir tool,”“spindle,” “tool body,” and the like as used in this specification maybe used to refer to the outer portion of the tool body, which comprisesa passageway lengthwise through the tool for holding and dispensing feedmaterial through the tool. This passageway, or throat, is generally theshape of a hollow cylinder. The hollow cylinder can be configured tohave a wider opening at the top of the tool for accommodating the augerand powder material and a smaller opening at the base of the tool wherethe feed material is dispensed from the tool. Thus, the shape of thethroat of the tool need not be consistent throughout the length of thetool throat and can be configured to converge from one lengthwise end ofthe tool to the other. As shown in FIG. 1, the throat of the tool cancomprise a first region which is the shape of a hollow cylinder of afirst diameter. This region can transition into a second region which isthe shape of a hollow cylinder of a second smaller diameter. Thetransition region can be a converging hollow cylinder or funnel shapedregion to allow the first and second region to be connected seamlessly.

Disposed within the tool body is an auger. In the context of thisspecification, the terms “auger,” “screw,” and “plunger” may be used torefer to a component of the tool that is disposed within the tool throatfor pushing or pulling material through the throat. Also within thisspecification, the auger can be considered a component of the frictionstir tool body. The auger can have the general shape of a screw withthreads, as shown in FIG. 1, or can be shaped in a spiral configurationsimilar to a spring. When disposed within the tool throat, there may beclearance between the auger and the inside surface of the tool throat toallow for the passage of feed material between the auger and the throat.In other embodiments, there is only enough space to allow for rotationof the auger without interference from the surface of the throat.Preferably, the auger and tool body or spindle are not attached to oneanother. Each is operably connected with means for rotating andtranslating the components relative to a substrate surface, such thatthe auger and tool can rotate at different speeds but translate relativeto the substrate at the same speed. It is preferred to keep the augerdisposed within the tool throat in a manner such that there is norelative translational movement between the auger and tool body.

Powdered materials can be feed into the top of the spindle using afluidized powder delivery system. Any type of powder delivery system canbe used in connection with the tools and systems of the presentinvention. For example, a gravity-fed powder feeder system can be used,such as a hopper. One such feed system is the Palmer P-Series VolumetricPowder Feeder from Palmer Manufacturing of Springfield Ohio, which iscapable of delivering feed material from 0.1-140 cu. ft. per hour, andwhich comprises a flexible polyurethane hopper, stainless steelmassaging paddles, 304 stainless steel feed tube and auger, 90-volt DCgearhead drive motor, flexible roller chain drive system, sealed drivetrain and cabinet, and solid state control and pushbutton controls. Thefeed system preferably comprises a reservoir for holding powder coatingmaterial, a mixer for mixing powder(s) added to the reservoir, and apassageway for delivering feed material from the hopper to the throat ofthe tool body. As feed material is dispensed into and from the tool,more feed material is delivered into the tool from the hopper. In thismanner, the feed material is continuously or semi-continuouslydelivered. The gravity-fed dispensing systems allow for feed material toautomatically be dispensed from the hopper to the friction stir toolduring use as soon as material within the tool is dispensed.

Feeding multiple powders into the spindle will allow for creation ofMMCs and alloys. MMC (metal-matrix composite) coatings can be formed inthe same manner as a wrought coating, including by having the matrixalloy and the reinforcement feed through the spindle. However, the MMCconsumable feed materials can be made by several methods, including butnot limited to mixing the matrix metal and reinforcement powders as feedmaterial, and in some cases mixing of the matrix and reinforcementfurther during the fabrication process.

In embodiments, a mix of powder types can be added to the hopper whichis operably connected with the stir tool. Alternatively, severaldifferent types of powder can be added individually to the hopper, thenmixed within the hopper and dispensed as a mixture to the friction stirtool during use. For example a metal powder and ceramic powder could befed into the spindle at the same time, from the same or separatehoppers, and upon consolidation/deposition the coating would be a metalmatrix composite (MMC). As used herein, the term “metal matrixcomposite” means a material having a continuous metallic phase havinganother discontinuous phase dispersed therein. The metal matrix maycomprise a pure metal, metal alloy or intermetallic. The discontinuousphase may comprise a ceramic such as a carbide, boride, nitride and/oroxide. Some examples of discontinuous ceramic phases include SiC, TiB₂and Al₂O₃. The discontinuous phase may also comprise an intermetallicsuch as various types of aluminides and the like. Titanium aluminidessuch as TiAl and nickel aluminides such as Ni₃Al may be provided as thediscontinuous phase. The metal matrix may typically comprise Al, Cu, Ni,Mg, Ti, Fe and the like.

Likewise, a first type of powder can be added to the hopper, dispensedthrough the tool, and applied to the surface of a substrate in a desiredmanner. Then, to produce a graded coating, a different type of powdercan be added to the hopper, dispensed through the tool and applied tothe substrate to provide a second layer of a different metalcomposition. This process can be repeated any number of times to formthe graded coating by successive addition of any number of variousmaterial compositions.

Various types of substrates may be coated using the friction-basedfabrication process of the present invention. For example, metalsubstrates comprising Al, Ni, Cu, Mg, Ti, Fe and the like may be coated.Furthermore, polymers and ceramics may be provided as the substrate. Forexample, the substrate may comprise a thermoplastic material.

Varying the ratio of the powder composition as a function of locationwill allow for deposition of coatings with graded compositions andproperties. Functionally graded coatings are desirable when variationsin mechanical and/or physical properties are desired as a function ofposition. Also grading the composition can be advantageous when joiningdissimilar materials. It is within the skill of the art to providedesired mixtures of different types of powder materials to accomplish aspecific type of coating.

For example, in embodiments aluminum powder is continuously feed intothe spindle at a specified rate using a fluidized feeding system. Thealuminum powder then comes into contact with the rotating auger screwwhich traps material in the open helical volume between the sleeve orbore inner diameter and the minor diameter of the helix. The rotation ofthe auger relative to the bore imparts a force on the powder whichconveys the powder into the stirring tool, as shown in FIG. 1. Thecontinuous conveyance of powder into the stirring tool by the augerforces powder through the stirring tool. The powder then exits thestirring tool and is consolidated and deposited as part of the fillermaterial due to the shearing action and frictional heating imparted bythe stirring tool.

The tool body and auger can be operably configured in multiple ways toachieve the functional results described in this specification. Beloware some of the features and their related design tasks which can beincorporated into the spindle.

Auger Screw Design

For material to be forced through the spindle the auger screw should bedesigned in such a way that pressure is exerted on the powder by thescrew. A significant amount of design knowledge exists in the metalpowder injection molding and extrusion literature. Polymer screwdesigns, e.g., can be found at:http://www.spirex.com/media/doc/The%20Basics%20of%20Good%20Extrusion%20Screw%20Design.pdf,which is hereby incorporated by reference herein in its entirety, andcan include screw designs such as the Xaloy brand extrusion screw,including the Efficient Screw or the Fusion Screw for example. Evenfurther, for example, non-limiting auger screw designs can include thoseshown in FIG. 2A. In embodiments, a twin screw design can also be usedwhere two screws cooperate together to push the feeder material throughthe tool throat. The design features of particular interest are theamount of pressure generated on the powder at the tool throat and therate at which powder is fed from the screw (e.g., auger) per revolutionor the volumetric pitch. The absolute rate at which powder is fedthrough the spindle will depend on the volumetric pitch and thedifference between the rotational velocities of the spindle and augerscrew.

As shown in FIG. 2B, a conical auger screw can also be used to push feedmaterial through the throat of the stirring tool in a continuous orsemi-continuous manner. Powder feed material can be delivered into theinterior conical portion of the powder auger screw preferably throughone or more inlets disposed on the upper portion of the auger screw. Dueto the conical design, the powder is pushed into the stirring tooldisposed below the auger.

Sleeve Design

The powder feeding system can comprise an auger screw and housing orbore, preferably modular components, capable of insertion into thethroat of the spindle. Both the screw and bore will likely wear with useand need to be replaced periodically and as such it may be desired thatthey not be permanently joined to the spindle. One embodiment providesfor the screw and bore to be mounted into a sleeve that will be keyedinto the spindle and fastened into place. During use, the powder feedmaterial can be dispensed into the bore within which the auger isdisposed. Feed material is then pushed through the bore to be dispensedon the substrate without coming into contact with the throat of the toolbody.

The sleeve, as shown in FIG. 1, occupies the volume between the spindleinner diameter and the auger screw and may also be keyed into thespindle and/or stirring tool. The sleeve provided mounting locations forsupport bearing for the auger screw as well as a mounting location forthe bore. The bore is in contact with some or all of the auger majordiameter. The bore can be a comprised of a different more wear resistantmaterial than the sleeve as rubbing of the auger and feed powder wearsthe bore.

Bore Design

The bore can be operably configured to accommodate bearings on one orboth the powder feed side and spindle to keep the screw from whipping orbecoming off-center. Proper selection of these bearings and the mannerin which they are housed will be a key to the long term success of thematerial feeding design.

Powder Feeding/Metering System

Powder filler material can be fed into the top of the rotating spindleby a fluidized powder dispensing system which can continuously andaccurately dispense powder. In preferred embodiments, two or moreseparate dispensing systems can be installed so that multiple powderscan be independently introduced to the system allowing for continuousvariation of composition. Employing a fluidized feeding will allow forfeeding powders of widely different particle sizes and shapes.

Continuous powder feeding makes the possibility of fabricating largecomplex 3D structures practical. The inventive approach isdifferentiated from all other digital manufacturing technologies in thatit enables solid-state deposition of wrought metal onto a substratefollowed by successive build-up of complex 3D structures. Unlikestate-of-the-art digital manufacturing, the approach described in thisapplication is based on wrought metal working technology which affordshigh deposition rates (200 lbs/hr in steel) and a large part envelope(multiple cubic meters), which are not offered by modified powdermetallurgy or fusion welding methods.

Digital manufacturing using friction-based fabrication tooling accordingto embodiments of the invention can include automated systems, such ascomputer aided design (CAD), e.g., comprising: a) tooling and afluidized powder delivery system in operable communication with thetooling; b) means for controlling (i.e., control system) one or morefunctions of the tooling and/or powder delivery system (such asrotational velocity of the tool body, rotational velocity of the auger,translational velocity of the tool, composition and flow rate of thepowder into the tooling and/or three-dimensional positioning of thetooling relative to the substrate); c) software for providinginstructions (whether previously programmed or comprising the capabilityto deliver real-time instructions) to the control system for the toolingregarding, e.g., rotational and/or translational speed,three-dimensional positioning of the tooling relative to the substrate,and/or composition and/or flow rate of the powder. The tooling for suchdesigns can include any friction stir tooling available.

Embodiments of the invention provide a friction stir system comprising:friction stir-based fabrication tooling; and a fluidized powder deliverysystem in operable communication therewith; wherein the powder deliverysystem is operably configured for continuously delivering a coatingmaterial into and through the tooling.

Specific embodiments of systems according to the invention include afriction stir-based fabrication tooling comprising: a non-consumablebody with a throat; a screw-type auger disposed in the throat forcontinuously delivering powder-type coating material through the throatof the tool body; one or more means for rotating the tool body at adesired first velocity and for rotating the auger at desired secondvelocity; and a shoulder for trapping and shearing a surface of coatingmaterial loaded on the substrate in a volume between the tool body andthe substrate. Such systems can comprise means for automaticallydispensing varying amounts of filler material into the tooling inresponse to variations in thickness of a substrate being processed. Forexample, as feed material is delivered through the tool body, more feedmaterial is automatically delivered into the tool body from a reservoir,e.g., hopper. As the tool translates over the substrate surface,variations in substrate thickness may be encountered by the tool, suchas the substrate being thinner in one portion. As the tool is depositingfiller material to the thinner portion of the substrate, more fillermaterial will be needed to fill the space between the substrate surfaceand the shoulder of the tool. A gauge can be used to determine when thesubstrate thickness is different and thus requires an accommodatingamount of filler material. More particularly, systems of the inventioncan comprise a thickness gauge for determining substrate thickness and acontrol system for varying the amount of filler material dispensed inresponse to detection of a pressure above or below a set pressurethreshold. Even further, such systems can comprise means for translatingthe tooling relative to a substrate in a desired CAD-drivenconfiguration.

Especially preferred tooling includes tools which have an internalthroat for delivering feed material through the tool for deposition on asubstrate and which have structure for forming and shearing a surface ofthe coating material deposited on the substrate, such as a shoulderfacing the substrate. Representative friction stir tools that can beused according to embodiments of the invention are shown in FIGS. 3A-B.As shown, filler material, such as in rod or powder form, can bedelivered through the throat of the tool with a plunger tool for pushingthe material toward the substrate. The plunger tool in preferredembodiments can be in the form of an auger. As the body of the tool, orspindle, is rotated, the consumable feed material is dispensed on thesurface of the substrate and the tool is translated across the surfaceof the substrate to deposit a layer of feed material as a coating on thesubstrate.

Methods, tools, and systems of the invention provide for freeformmanufacturing of 3-D parts having a wrought microstructure. Inembodiments, friction-based fabrication may be a solid state,friction-based coating method that can be used, for example, to meetnaval needs for welding, coating and repair of aluminum vessels.Friction-based fabrication according to the invention uses shear-inducedinterfacial heating and plastic deformation to deposit wrought metaland/or metal matrix composite (MMC) coatings on substrates. Theadditive-type fabrication processes of embodiments of the invention issuitable for direct manufacturing of parts by computer assisted design(CAD) techniques, otherwise referred to as digital manufacturing.Methods, tooling, and systems of the present invention are capable ofproviding metal substrates comprising a digitally manufacturedfunctionally graded coating exhibiting a layered wrought microstructurewith no discrete interface between layers.

Specific methods of the invention include friction-based fabricationmethods comprising: providing an amount of coating material in powderform; delivering the coating material into a throat of a friction stirtool; pushing the coating material through the tool using an auger;dispensing the coating material onto a substrate; and forming andshearing a surface of the coating material on the substrate usingcompressive loading and frictional heating. The coating material can bedelivered into the throat of the tool from a hopper and by gravity inresponse to coating material exiting the tool.

Once the coating has been deposited onto the surface of the substrate,e.g., using the solid-state friction deposition method, it may then befriction stir processed to adhere the coating to the surface of thesubstrate and refine the coating microstructure. The goal of thefriction stir process is to produce a homogenous coating with a bondstrength approaching the ultimate tensile strength of the base alloy.For example, friction stir processing of an Al—SiC rib was performedusing a stirring tool with an unthreaded cylindrical pin. The use ofthis stirring tool resulted in some variation in the local SiC volumefraction and a channel at the bottom of the FSP zone. The quality of thefriction stirred regions of the substrates may be optimized, includingeliminating any channel present along the length of the friction stirpath. Elimination of the channel may be achieved by using a frictionstir tool with a threaded pin. Subsequent processing of the same MMCcoating and 5083 Al substrate with such improved tool geometry producedhomogeneous coatings without a channel. By modifying the stirring toolgeometry, coated substrates may be produced without channels through theuse of a threaded-tapered stirring tool.

Methods of the invention can further comprise altering powdercomposition during deposition to provide a coating with a desiredcomposition gradation.

In embodiments, a method of preparing a metal part is provided whichcomprises depositing multiple layers of coating material on a substratein a selected three-dimensional configuration using continuouspowder-fed friction fabrication tooling. In such methods, duringdepositing, the powder composition can be selectively modified to obtaingradations in the 3D configuration with no discrete interface betweencoating layers to prepare a functionally graded metal part. Functionallygraded substrates formed using any of the tools, methods, or systems ofthe present invention are also provided.

FIG. 4 provides a schematic diagram of tooling, systems, and methods forpreparing functionally graded substrates. As shown in FIG. 4, 3-Ddigital manufacturing by deposition of successive wrought layers is madepossible by embodiments of the present invention. As shown, feedmaterial can be continuously or semi-continuously dispensed onto asubstrate through the throat of a friction stir tool according to adesired CAD configuration. Material is added to the substrate using anyfriction fabrication tool, but especially preferred is tooling capableof delivering consumable feed material through the throat of the tool.Using feed material in powder form, the feed material can be of one or amixture of types of material that is added to a feed delivery system andcontinuously feed into and through the tool throat. In embodiments wherean auger is used to push feed material through the spindle, the feedmaterial can be contained within a bore in which the auger is disposedwithin the tool body. In this manner, the feed material comes intocontact with the auger but not the interior surface of the tool body.The auger is rotated within the tool throat to push the feed materialthrough the tool body and onto the substrate in the desired CAD pattern.The tool is also preferably rotated and comprises a shoulder to trapfiller material between the tool body and the substrate, under which asurface of the coating is formed and finished by shearing action fromthe tool body. As the tool is translated across the substrate in thedesired CAD pattern, a coating is formed on the substrate in the desiredpattern. As shown, the tool need not translate in a straight line andcan translate relative to the substrate in any pattern, preferablyaccording to the CAD program.

FIG. 5 is a schematic drawing illustrating another embodiment of thecontinuous feed system of the invention, which uses a rolling mill typemechanism to deliver feed material into the spindle. As shown, arod-type filler material can be fed into the throat of the stirring toolusing counter-rotating feed rollers. Preferably, the filler material rodco-rotates with the stirring tool. In embodiments, and as shown in FIG.5, the rod filler material has a square cross section and cooperateswith the interior of the stirring tool, which has a square cross sectionabout the same size or just slightly larger than the rod filler materialin order to accommodate the filler material in the throat of the tool.During use, due to the shape of the filler material and correspondingshape of the interior of the tool, normal forces act on the fillermaterial to cause the filler material to rotate with the stirring tool.The feed material is disposed between two feed rollers which rotatetoward one another causing the filler material to be pulled into thespace between the rollers and toward the stirring tool. As the feedrollers rotate, the feed material is continuously provided into thethroat of the tool.

The present invention has been described with reference to particularembodiments having various features. It will be apparent to thoseskilled in the art that various modifications and variations can be madein the practice of the present invention without departing from thescope or spirit of the invention. One skilled in the art will recognizethat these features may be used singularly or in any combination basedon the requirements and specifications of a given application or design.Other embodiments of the invention will be apparent to those skilled inthe art from consideration of the specification and practice of theinvention. Where a range of values is provided in this specification,each value between the upper and lower limits of that range is alsospecifically disclosed. The upper and lower limits of these smallerranges may independently be included or excluded in the range as well.As used in this specification, the singular forms “a,” “an,” and “the”include plural referents unless the context clearly dictates otherwise.It is intended that the specification and examples be considered asexemplary in nature and that variations that do not depart from theessence of the invention are intended to be within the scope of theinvention. Further, the references cited in this disclosure areincorporated by reference herein in their entireties.

1. A friction-based fabrication tool comprising: a non-consumable toolbody with a throat having an interior cross section shaped to impartnormal forces on a feed material disposed therein when rotated; and feedrollers disposed above the non-consumable tool body and comprising meansfor rotating the feed rollers toward one another such that feed materialdisposed perpendicularly to the feed rollers is pulled between the feedrollers and is delivered continuously through the throat of the toolbody during use; wherein the tool body comprises a surface for trappingfeed material loaded on the substrate in a volume between the tool bodyand the substrate and for forming and shearing a surface of a coating onthe substrate with frictional heating and shear loading.
 2. The systemof claim 1, wherein a cross section of the throat is square and sized toaccommodate a complementary shaped and sized rod-type feed material.